The present invention relates to a memory devices, and more particularly, to memory controllers and systems.
Semiconductor memory devices may include random access memory (RAM) that can freely read/write data but may lose stored data when power is cut off, a read only memory (ROM) that may not lose data once programmed and may retain the data even if power is cut off, and flash memory devices that may include factors of both RAM and ROM. A card type package of a flash memory device may be called a memory card (or a flash memory card). The memory card has come into wide use as a recording medium for digital devices such as digital cameras and/or portable music players. Also, USB memory, which may include a flash memory device packaged with a USB connector, may be perceived as a convenient data exchange medium for personal computers (PC) because it may present a preferable alternative to floppy disks. Recently, some systems have a flash memory device mounted on a mother board of a PC for use as a BIOS memory.
Flash memory cards have been used as auxiliary data storage devices in earlier systems where slow reading and writing rates of 10 MB/s or less were sufficient. However, as demands for mass-storage increase, flash memory cards ideally include a fast access rate for large-capacity data management and can perform good enough to substitute for an existing hard disk. Therefore, a buffer memory, such as an SRAM or a DRAM, may be needed. A buffer memory may have a capacity several times greater than that of a buffer memory used in early flash memory cards. However, additional software may be needed to manage the increasing capacity. In general, even a flash memory card having a buffer memory with small capacity may need a response time ranging from tens of microseconds (μs) to hundreds of microseconds. Thus, response time with respect to a host command may increase as the buffer memory increases in capacity. Accordingly, a technology for reducing the response time with respect to the host command may be beneficial.